On 11/22/2018 02:43 PM, Kazlauskas, Nicholas wrote:
> On 11/22/18 2:39 PM, Grodzovsky, Andrey wrote:
>>
>> On 11/22/2018 12:34 PM, Nicholas Kazlauskas wrote:
>>> [Why]
>>> Atomic check can't truly be non-blocking if amdgpu_dm is waiting for
>>> hw_done and flip_done in atomic check. This introduces waits when
>>> any previous non-blocking commits queued work on a worker thread and
>>> a new atomic commit attempts to do another full update/modeset.
>>>
>>> [How]
>>> Drop the waits and move the global lock acqusition into atomic check.
>>>
>>> This is fine to do since commit tail waits for these dependencies
>>> before calling amdgpu_dm_atomic_commit_tail.
>> Note that drm_atomic_helper_wait_for_dependencies waits only on all
>> preceeding commits that touch the same CRTC
>> while our custom do_aquire_global_lock wait on ALL previous commits in
>> the system - even on other CRTCS. As far as I can
>> remember that was important because we have global dc_state context
>> which must be protected for access/modifications while
>> looks like DRM assumes unrelated CRTCs can be modified concurrently.
>> Try to verify that latest display code will not be broken by this
>> relaxation of synchronization.
>>
>> Andrey
> This is a good point.
>
> What we should really be doing instead here is locking anything that can
> modify dc->current_state from within atomic commit tail. Serializing
> commits into a queue could work too.
This is a possibility by then you have to duplicate
drm_atomic_helper_commit with only once change which
is to substitute system_unbound_wq with you costume WQ. Alternatively
propose a change to update drm_atomic_helper_commit
to allow WQs as parameter.
Andrey
>
> Either should fix non-blocking support.
>
> Nicholas Kazlauskas
>
>>> This is only safe as long as DC never queries anything from within
>>> current_state when doing validation in atomic_check. This is the
>>> case as of writing, but any future uses of dc->current_state from
>>> within atomic_check should be considered incorrect.
>>>
>>> Cc: Harry Wentland <harry.wentland@xxxxxxx>
>>> Cc: Leo Li <sunpeng.li@xxxxxxx>
>>> Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@xxxxxxx>
>>> ---
>>> .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 58 ++-----------------
>>> 1 file changed, 6 insertions(+), 52 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>> index 3ae438d9849f..fe21bb86b66a 100644
>>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>> @@ -5078,57 +5078,6 @@ void dm_restore_drm_connector_state(struct drm_device *dev,
>>> dm_force_atomic_commit(&aconnector->base);
>>> }
>>>
>>> -/*
>>> - * Grabs all modesetting locks to serialize against any blocking commits,
>>> - * Waits for completion of all non blocking commits.
>>> - */
>>> -static int do_aquire_global_lock(struct drm_device *dev,
>>> - struct drm_atomic_state *state)
>>> -{
>>> - struct drm_crtc *crtc;
>>> - struct drm_crtc_commit *commit;
>>> - long ret;
>>> -
>>> - /*
>>> - * Adding all modeset locks to aquire_ctx will
>>> - * ensure that when the framework release it the
>>> - * extra locks we are locking here will get released to
>>> - */
>>> - ret = drm_modeset_lock_all_ctx(dev, state->acquire_ctx);
>>> - if (ret)
>>> - return ret;
>>> -
>>> - list_for_each_entry(crtc, &dev->mode_config.crtc_list, head) {
>>> - spin_lock(&crtc->commit_lock);
>>> - commit = list_first_entry_or_null(&crtc->commit_list,
>>> - struct drm_crtc_commit, commit_entry);
>>> - if (commit)
>>> - drm_crtc_commit_get(commit);
>>> - spin_unlock(&crtc->commit_lock);
>>> -
>>> - if (!commit)
>>> - continue;
>>> -
>>> - /*
>>> - * Make sure all pending HW programming completed and
>>> - * page flips done
>>> - */
>>> - ret = wait_for_completion_interruptible_timeout(&commit->hw_done, 10*HZ);
>>> -
>>> - if (ret > 0)
>>> - ret = wait_for_completion_interruptible_timeout(
>>> - &commit->flip_done, 10*HZ);
>>> -
>>> - if (ret == 0)
>>> - DRM_ERROR("[CRTC:%d:%s] hw_done or flip_done "
>>> - "timed out\n", crtc->base.id, crtc->name);
>>> -
>>> - drm_crtc_commit_put(commit);
>>> - }
>>> -
>>> - return ret < 0 ? ret : 0;
>>> -}
>>> -
>>> void set_freesync_on_stream(struct amdgpu_display_manager *dm,
>>> struct dm_crtc_state *new_crtc_state,
>>> struct dm_connector_state *new_con_state,
>>> @@ -5793,7 +5742,12 @@ static int amdgpu_dm_atomic_check(struct drm_device *dev,
>>> if (ret)
>>> goto fail;
>>>
>>> - ret = do_aquire_global_lock(dev, state);
>>> + /*
>>> + * This should be replaced with finer locking on the
>>> + * on the appropriate resources when possible.
>>> + * For now it's safer to grab everything.
>>> + */
>>> + ret = drm_modeset_lock_all_ctx(dev, state->acquire_ctx);
>>> if (ret)
>>> goto fail;
>>>
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